1. Field of the Invention
The invention provides a lightweight modular composite building assembly system with components capable of sustaining heavy axially applied loads.
2. Description of the Related Art
Polymer foam materials, e.g., sheets or blocks of low density expanded polystyrene, polyurethane and the like, have been widely used in the construction industry for purposes of building insulation. Plastic foam in the form of panels or foamed-in-place polyurethane has been used, for example, to provide an insulative wall or roof sheathing material, as perimeter insulation for floor slabs, as an insulative core layer sandwiched between structural components such as plywood, wall board or metal, as disclosed in U.S. Pat. No. 3,583,123, or as insulative layers surrounding poured concrete, as for example disclosed in U.S. Pat. No. 5,664,382.
It has also been proposed in the prior art to utilize plastic foam materials in combination with other structural components to prepare structural building panels or blocks which are said to be capable of structural rigidity especially from lateral loads or other stresses applied to them. Examples of such structural components may be found in U.S. Pat. No. 5,638,651 which discloses an interlocking insulated panel having an expanded polystyrene core sandwiched and glued between oriented strand board (OSB) and further containing a pair of metal channels glued to opposite sides of the core and partially embedded in the core. The metal channels are said to impart structural strength to the panel. U.S. Pat. No. 4,903,446 discloses a prestressed plastic foam structural member prepared by forming a grid-work of rope-like or wire tendons maintained in a tension condition within a mold, and encapsulating the grid-work with expandable plastic foam to form a lightweight structural member.
Also, U.S. Pat. No. 4,351,870 discloses a building panel material comprising a centrally disposed convoluted sheet stiffening layer of high strength material, such as metal or plastic, laminated on each side with an adhered sheet of expanded plastic material such that the expanded plastic sheet contacts the convoluted crests and troughs of the centrally disposed sheet. The panel may also contain coatings on the outer foamed plastic surfaces thereof which are of a decorative or weather-proofing nature, as well as combustion-inhibiting layers positioned on one or both sides of one or both expanded plastic sheet layers.
Further, U.S. Pat. No. 5,448,862 discloses a prefabricated foamed plastic staircase where vertical slots are provided for the insertion of reinforcing steel rods meant for embedment in concrete beams below the surface to provide stiffening for the overall structure but no assistance to the function loading on the tread surfaces.
Other related structures are disclosed in U.S. Pat. Nos. 4,159,681; 4,241,555; 4,558,550; 4,611,450; and 4,774,794.
In applications such as described above, the expanded plastic material serves two primary roles:
a) an insulation layer which imparts both insulative value and moisture barrier properties to the structure, and/or
b) a matrix imparting three-dimensional shape to the structure and providing a platform for mounting or assembling structural components and/or fire retardant or finishing layers.
In none of these applications are the main structural components intended for the primary purpose of supporting or bracing axial loads directly applied to an encapsulated rigid structure, nor is the expanded plastic material by itself intended to, or capable of, supporting high compressive or axial loads applied thereto, or even capable of contributing significantly to the strength of the main structural components which are designed into such systems as the load and stress-bearing components. It is obvious that, in all of the prior art, the general intent of the foam is to provide diaphragm rigidity to a planar configuration from lateral forces, with no active purpose in the support of directly applied longitudinal axial loading in compression. And while such diaphragm rigidity may have been accomplished, the end product results are limited to purposes of rigid building enclosure rather than as the main building structural supporting elements.
For example, consider a steel wire mounted vertically between the plates of a press. The wire will initially resist a certain amount of compressive axial force applied. As more pressure is applied, the wire will strain and begin to buckle and eventually bend or break at the point of compressive tensile failure. Now consider the wire inserted longitudinally at the axis of a cylinder of STYROFOAM(trademark) plastic about the size of a wooden thread spool such that the wire tips are exposed at the base and top of the cylinder. As the main support for the structure, the axially disposed wire will be subjected to the same forces as described for the unsupported wire, but will to some degree be laterally supported by the STYROFOAM(trademark) matrix. Since the styrene foam can support only about 20-25 lbs per square inch compressive force after 10% deformation, the wire remains the main structural component. The tendency of the wire to buckle is, however, somewhat restrained by forces generated as the wire bows and compresses the surrounding foam in the direction of bowing, but there is no support for the wire on the side opposite the direction of bowing and the wire will eventually rupture the compressed foam and fail as described above. This is essentially the same phenomena involved with the prior art structures described above where structural layers are laminated to or encapsulated within foam layers and the resulting structure subjected to stress.
Now consider that same steel wire coated with an adhesive and inserted longitudinally at the axis of the STYROFOAM(trademark) cylinder such that the wire tips are exposed at the base and top of the cylinder and the shaft is circumferentially bonded to the foam. As the main support for the structure, the axially disposed wire will be subjected to the same forces as described for the unbonded wire, but the tendency of the wire to buckle is now restrained by foam matrix compressive resistance on the bowing side, and tensile forces on the opposite side between wire and foam because of the adhesive. Also, the circumferentially bonded adhesive on the wire itself will resist elongation and contraction of the wire""s surface to provide additional stiffening and stability, further resisting the wire""s tendency to buckle under compressive axial load.
It is therefore an object of the present invention to utilize the foam matrix itself, in combination with an adhesion to a fully encapsulated rigid sheet or membrane, for the prime purpose of laterally bracing said membrane to support high compressive axial load with minimum material expenditure. By volume, in the present invention the system is 88xc2xd% air, by which is created a structural matrix that laterally braces an axial-loaded membrane to produce ultimate strength. Therein, structural performance is maximized with minimum material.
It is a further object of the present invention to provide a high strength but extremely light weight axial load-bearing structural foamcore panel, where the strength to weight ratio can exceed 1000 to 1.
Another object of the present invention is to provide structural load-bearing wall panels wherein the encapsulated rigid sheet or membrane structure is in the form of longitudinally corrugated sheets with hollow tubular sections which are continuous across the entire dimension of the panels and establish a functionally homogeneous composite structure.
Yet another object of the present invention is to provide pairs of said corrugated sheets which, when reversed and mated together, form hollow tubular sections with perforated surfaces for the aspiration of process gases, the additional structural resistance against buckling, and the eventual installation of utilities related to panel erection in building construction.
Another object of the present invention is to provide this same wall panel configuration in the horizontal or oblique application to resist laterally applied loads, wherein a panel configuration similar to a wall panel may be used as roof panels or the like.
Still another object of the present invention is to provide filler floor beams which may be longitudinally subdivided sections of said wall or roof panel configurations with the longitudinal tubular sections horizontal and vertically aligned.
And another object of the present invention is to provide floor beams comprising a continuous longitudinal rigid hollow tubular section encapsulated in a rectangular volume of foam with a square cross-section, with three vertical sheet or membrane plates attached to the tube, with two at respectively opposite side tangent points and the third bisecting the hollow tube and projecting above and below it, with all such plates continuous and the full height of the rectangular volume composite.
And yet another object of the present invention is to provide a premolded staircase with successive and continuous rigid sheet or membrane stair profile stringers, made of a high-strength material, divided by, laminated to, and laterally braced by larger thicknesses of foamcore material such that the end result is a completed ultra-lightweight staircase assembly.
The above and other objects of the present invention and the attendant advantages are accomplished by maximizing the efficiency of a primary structural material. In the present invention, an axially-loaded sheet or membrane at 65 lb density can resist buckling by being laterally braced against failure with a structural foam matrix at 1.5 lb density. The resulting composite is extremely lightweight and economical, two highly desirable features for building construction components. In principle, the total encapsulation and adhesion of a rigid columnar material by a structural matrix which by volume is largely air produces this phenomenon. As opposed to the prior art where rigid stressed-skin structures are external only, herein the total encapsulation is internal and doubles the surface contact area for the beneficial lateral bracing effect. The theoretical advantage relative to the prior art is that this bracing effect will make the skin twice as strong or facilitate only half as much material to support the same weight under axial loading conditions. This advantage over the prior art implies an unprecedented potential for architectural expression in building formations, and establishes the basis for the embodiments of the present invention.
In accordance with the major embodiment of the present invention, an elongated rigid sheet or membrane, as the primary supporting structure capable of sustained axial stress, is encapsulated within, bonded to, and laterally braced by a foam core material to create a lightweight modular composite building frame component, wherein extremities of the rigid sheet or membrane may be configured on said frame component edges for tools-free interlock with adjacent horizontally and/or vertically aligned building components.
In accordance with another embodiment of the present invention, a floor system is provided comprising two connectors and a floor beam connected between the two connectors. The floor beam comprises a rigid hollow tube encased by an expanded polymer foam with openings into opposite ends of the tube. This hollow tube has three vertical plates attached, two at respectively opposite side tangent points and the third bisecting the tube and projecting above and below it, with all such plates continuous to the extremities of the polymer foam volume. The two connectors each have a pipe-shaped lateral extension that extends into opposite end openings of the tube thereby supporting the floor beam on the connectors.
In accordance with another method of the present invention, a method of manufacturing a wall panel is provided comprising rigid material which is shaped such that longitudinal tubular sections are formed along the entire length of the wall panel. These tubular sections are intended to do the following: they constitute the axial-loaded structure, the circular surfaces are perforated to form breathing vents for the aspiration of process gases generated in the molding process, and after panel erection these tubular sections establish a continual internal chase opportunity for the installation of utilities. The overall composite wall panel configuration is also used as a roof panel except longer continuous lengths are required than those normally associated with wall heights. Here, the loading is applied lateral or oblique to the main panel longitudinal axis, as well as that of the individual panel sheets, however the bracing action of the foam layer and the geometry of the panel configuration is sufficient to resist such lateral loads.
In accordance with yet another method of the present invention, a pre-molded laminate composite staircase configuration comprising continuous and successive rigid sheet or membrane stair profile stringers with continuous thin gage steel bands laminated thereto, divided by and laminated to larger continuous thicknesses of foam core material of the same stringer profile such that the end result is a completed laminate composite assembly which can function as a prefabricated structural staircase that is extremely lightweight, economical and easy to install.